Drainage canals: What name is given to canals that are specifically constructed to relieve and convey excess water from water-logged or poorly drained areas?

Introduction / Context:
In irrigation and land reclamation, not all canals are for supply; many are built to evacuate excess water. Persistent water-logging reduces crop yields, damages soil structure, and promotes salinity—hence the need for engineered drainage canals.

Given Data / Assumptions:

• Area suffers from high water table and/or perched water due to seepage, rainfall, or over-irrigation.
• Objective is to lower the water table and remove excess surface/subsurface water.
• Canal types are distinguished by alignment purpose and function.

Concept / Approach:

Drainage canals (drains) collect and convey unwanted water from fields and low areas to natural outfalls or sumps, thereby reclaiming land productivity. They are designed for self-cleansing velocities and adequate capacity during wet periods.

Step-by-Step Solution:

Verification / Alternative check:

Standard irrigation engineering texts define drains as channels built for removal of excess water, distinct from irrigation supply canals.

Why Other Options Are Wrong:

Inundation canals draw irrigation water directly from rivers during floods; valley and contour canals describe supply alignment strategies; ridge canals run along ridgelines to serve command areas.

Common Pitfalls:

Confusing mixed systems where combined supply–drain channels exist; not accounting for maintenance to avoid silting in flat terrains.

Final Answer:

Drains (drainage canals)